Recent years have seen a rapid increase in the number of patients with pruritic symptoms as from atopic dermatitis, atopic conjunctivitis and senile xerosis. These diseases are accompanied by an intense itch sensation of obscure etiology and itch-evoked scratching behavior is believed to induce inflammations in mucous membranes or skin. Therefore, eliminating an itch sensation is crucial to the elimination of those symptoms.
Pharmaceutical preparations conventionally used to treat chronic dermatitis include steroids for external application, antihistamines and antiallergics. However, the use of steroids is restricted for the side effects they may cause as a result of prolonged continued use, and no antihistamines or antiallergics have been obtained that are completely satisfactory in terms of therapeutic efficacy.
Heretofore, antipruritics have been assessed by administering histamine, serotonin and other pruritogens into the skin of animals and measuring their itch-evoked scratching behavior. However, it was recently reported that the manifestation of an itch due to pruritic symptoms as in atopic dermatitis is not simply the reaction caused by histamine, etc. that are released from mast cells (J. Dermatological Science 25, 20-28, 2001).
Therefore, it is desired to develop antipruritics that depend on a new mechanism of action for preventing and treating pruritic symptoms as in atopic dermatitis.
A prostaglandin has been reported to be a prurigenic component (J. Am. Acad. Dermatol. 47, 28-32, 2002) but its use as an antipruritic is not known.